Unworked continuously cast heat-treatable aluminum alloy plates

ABSTRACT

The present disclosure relates to methods of producing heat-treatable as-cast plate, and products based on the same. Generally, the new methods comprise continuously delivering a molten aluminum alloy having at least one of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu) to a molten belt caster, continuously solidifying the molten aluminum alloy into an aluminum alloy plate via the horizontal belt caster, then continuously discharging the aluminum alloy plate at an exit of the horizontal belt caster, and then quenching the discharged aluminum alloy plate via a quenching apparatus located proximal the exit of the horizontal belt caster.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims the benefit of priority of U.S. Provisional Patent Application No. 62/412,554, filed Oct. 25, 2016, entitled “UNWORKED CONTINUOUSLY CAST HEAT-TREATABLE ALUMINUM ALLOY PLATES”, which is incorporated herein by reference in its entirety.

BACKGROUND

Aluminum alloy plate may be produced by casting an ingot, scalping and homogenizing the ingot, hot rolling the ingot to an intermediate or final gauge, optionally with cold rolling of the an intermediate gauge to the final gauge. Working of the product by rolling generally imparts texture and residual stresses to the final rolled product.

SUMMARY OF THE DISCLOSURE

Broadly, the present patent application relates to methods of producing heat-treatable as-cast plate, and products supplied to the customers based on the same. In one approach, and referring now to FIG. 1, a method includes the steps of continuously delivering a molten aluminum alloy to a delivery tip (2) of a horizontal belt caster (1).

The molten aluminum alloy comprises a sufficient amount of at least one of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu) to promote formation of strengthening precipitates. The horizontal belt caster (1) is used to continuously solidify the molten aluminum alloy into an aluminum alloy plate. The aluminum alloy plate is continuously discharged from an exit of the horizontal belt caster (1), generally at a casting rate of from 1 inch to 150 inches per minute (e.g., from 2 to 20 inches per minute). The discharged aluminum alloy plate generally has a final gauge of from 0.25 inch to 5.0 inches (e.g., from 1.0 to 5.0 inches). The discharged aluminum alloy plate is quenched, via a quenching apparatus (3), located proximal the exit of the horizontal belt caster, thereby producing an as-cast heat-treatable aluminum alloy plate (4). The quenching comprises contacting outer surfaces of the discharged aluminum alloy plate with a quenching media. In the illustrated embodiment shown in FIG. 1, air jets are used, but any suitable quenching media can be used, including any suitable fluid, such as air, water, a mixture of air and water, or any other suitable liquid or gas, or mixture thereof. The continuously cast heat-treatable plate is then sawed into applicable pieces via plate saw (5).

In one embodiment, a method includes artificially aging the as-cast heat-treatable aluminum alloy plate, thereby developing strengthening precipitates within the as-cast heat-treatable aluminum alloy plate. Since the aluminum alloy plate is quenched at the exit of the caster (1), no additional solution heat treatment may be required prior to artificial aging (i.e., the method may be free of a separate/dedicated solution heat treatment step). Artificial aging may be accomplished by heating the as-cast heat-treatable aluminum alloy plate in a suitable furnace or other heating device for a time sufficient to develop a sufficient volume (including a sufficient size and distribution) of the strengthening precipitates. In one embodiment, the as-cast heat-treatable aluminum alloy plate is artificially aged at a temperature of from 275° to 450° F. In one embodiment, the as-cast heat-treatable aluminum alloy plate is artificially aged for from 1 to 20 hours. Any number of artificial aging steps may be used to precipitation harden the as-cast heat-treatable aluminum alloy plate.

The strengthening precipitates may be developed within the matrix of the as-cast heat-treatable aluminum alloy. The strengthening precipitates are generally coherent (to the matrix) phases, and the strengthening precipitates generally include at least one of silicon, copper, magnesium and/or zinc. The coherent phases generally have an average size of from 10 nanometers to 1 micron. In one embodiment, the coherent phases have an average size of not greater than 100 nanometer. Due to the composition of the molten aluminum alloy, the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 5 ksi higher than the naturally aged strength (T3). As used herein, “peak strength” means processing to a T6 temper, as per ANSI H35.1 (2009), and within 1 ksi (+/−) of the highest strength that can be achieved via artificial aging. As used herein, naturally aged strength means processing to a T3 temper as per ANSI H35.1 (2009). Strength and elongation are measured in accordance with ASTM E8 and B557. In one embodiment, the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 7.5 ksi higher than the naturally aged strength (T3). In another embodiment, the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 10 ksi higher than the naturally aged strength (T3). In yet another embodiment, the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 12.5 ksi higher than the naturally aged strength (T3). In yet another embodiment, the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 15 ksi higher than the naturally aged strength (T3), or higher.

The as-cast heat-treatable aluminum alloy plate also generally comprises good ductility for a thick, as-cast product. In one embodiment, the as-cast heat-treatable aluminum alloy plate realizes an elongation of at least 0.5%. In another embodiment, the as-cast heat-treatable aluminum alloy plate realizes an elongation of at least 1%. In another embodiment, the as-cast heat-treatable aluminum alloy plate realizes an elongation of at least 2%. In another embodiment, the as-cast heat-treatable aluminum alloy plate realizes an elongation of at least 3%. In another embodiment, the as-cast heat-treatable aluminum alloy plate realizes an elongation of at least 4%, or higher.

As shown in FIG. 1, the as-cast heat-treatable aluminum alloy plate is generally not worked after casting. Thus, in one embodiment, a method includes maintaining the as-cast grain structure of the as-cast heat-treatable aluminum alloy plate. Development of strengthening precipitates does not materially affect the as-cast grain structure of the as-cast heat-treatable aluminum alloy plate. Thus, after any artificial aging step, the heat-treatable aluminum alloy plate generally comprises the as-cast grain structure with the strengthening precipitates. In one embodiment, a method includes providing the as-cast heat-treatable aluminum alloy plate to a customer, wherein the as-cast heat-treatable aluminum alloy plate has the as-cast grain structure with the strengthening precipitates. In one embodiment, the maintaining the as-cast grain structure step comprises forgoing hot or cold working of the as-cast heat-treatable aluminum alloy plate after the continuously casting step.

In one approach, an as-cast aluminum alloy plate has a thickness of from 0.25 inch to 5.0 inches, and the as-cast aluminum alloy plate comprises at least 0.5 wt. % of at least one of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu). In one embodiment, an as-cast plate has a dendritic microstructure. In one embodiment, an as-cast aluminum alloy plate has a secondary dendritic arm spacing of from 30 to 150 microns in all of the longitudinal (L), the long-transverse (LT) and the short-transverse (ST) directions of the as-cast aluminum alloy plate. In one embodiment, an as-cast aluminum alloy plate has equiaxed grains and is generally free of elongated grains.

As used herein, “dendritic microstructure” means a branching microstructure formed during solidification wherein the branches form from an initial solidified nucleus, and maintain generally the same crystallographic orientation as the nucleus from which they are formed.

As used herein, “secondary dendritic arm spacing” means the spacing between the centers of the branches in a dendritic microstructure.

As used herein, “equiaxed grains” means grains having a grain aspect ratio of ≤2:1 in all of the L, LT and ST directions, as measured using the linear intercept method on representative micrographs of the as-cast aluminum alloy plate.

As used herein, “elongated grains” means any grains that are not equiaxed grains.

As used herein, “free of elongated grains” means an as-cast aluminum alloy plate comprises not greater than 5 vol. % of elongated grains.

The feedstock used to produce the aluminum alloy may be any suitable feedstock for producing an aluminum alloy, such as any conventional feedstock used to produce a 2xxx, 6xxx, 7xxx, or 8xxx(HT) aluminum alloy. Thus, in one embodiment, the feedstock is a conventional 2xxx, 6xxx, 7xxx, or 8xxx(HT) feedstock.

Further, it has been uniquely found that the molten aluminum alloy used to produce the as-cast heat-treatable aluminum alloy plate can be produced from aluminum alloy scrap. Thus, in one aspect, the method includes melting an aluminum alloy scrap feedstock, thereby producing a molten aluminum alloy for the horizontal belt caster, where the aluminum alloy scrap feedstock comprises a combination of at least two different aluminum alloy materials. With the proper mixture of aluminum alloy scrap, a heat-treatable as-cast aluminum alloy plate may be produced. Further, since scrap materials are used, in many instances, no additional additives may be required to produce the as-cast heat-treatable aluminum alloy plate.

In one approach, the scrap feedstock comprises at least two different classes of aluminum alloys. For instance, the at least two different classes of aluminum alloys may be selected from the following aluminum alloy series: 1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, and 8xxx aluminum alloys. In one embodiment, the at least two different classes of aluminum alloys are selected from the following aluminum alloy series: 3xxx, 4xxx, 5xxx, 6xxx, and 7xxx aluminum alloys. In one embodiment, the aluminum alloy scrap comprises at least two of 3xxx, 4xxx, and a 6xxx aluminum alloy scrap, optionally with 5xxx aluminum alloy scrap. In one embodiment, at least 50 wt. % of the scrap is a non-heat-treatable alloy, such as at least 50 wt. % of 3xxx, 4xxx and/or 5xxx aluminum alloy scrap, the remainder being heat-treatable alloy scrap, such as one or more of 6xxx and/or 7xxx aluminum alloy scrap. Several different ones of any class of aluminum alloy may be used to make-up the scrap feedstock (e.g., multiple different 3xxx, multiple different 4xxx, multiple different 5xxx, and/or multiple different 6xxx aluminum alloys may be used to create the feedstock).

In one embodiment, the scrap feedstock comprises (or consist of) at least two different aluminum alloys from the same class. For instance, a scrap feedstock may include at least two different 6xxx aluminum alloys. In another embodiment, a scrap feedstock may include at least two different 7xxx aluminum alloys. In yet another embodiment, a scrap feedstock may include at least two different 2xxx aluminum alloys. In another embodiment, a scrap feedstock may include at least two different 8xxx aluminum alloys, wherein at least one of the 8xxx aluminum alloys is a heat-treatable aluminum alloy. Other scrap feedstock combinations may be used.

The 1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, and 8xxx aluminum alloys are defined by the Aluminum Association document “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” (2015) (a.k.a., the “Teal Sheets”), incorporated herein by reference in its entirety. 1xx, 2xx, 3xx, 4xx, 5xx, 7xx, 8xx and 9xx aluminum casting and ingot alloys are defined by the Aluminum Association document “Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingot” (2009) (a.k.a., “the Pink Sheets”), incorporated herein by reference in its entirety.

As used herein, a “1xxx aluminum alloy” is an aluminum alloy comprising at least 99.00 wt. % Al, as defined by the Teal Sheets. The “1xxx aluminum alloy” compositions include the 1xx alloy compositions of the Pink Sheets.

A 2xxx aluminum alloy is an aluminum alloy comprising copper (Cu) as the predominate alloying ingredient, except for aluminum. The 2xxx aluminum alloy compositions include the 2xx alloy compositions of the Pink Sheets.

A 3xxx aluminum alloy is an aluminum alloy comprising manganese (Mn) as the predominate alloying ingredient, except for aluminum.

A 4xxx aluminum alloy is an aluminum alloy comprising silicon (Si) as the predominate alloying ingredient, except for aluminum. The 4xxx aluminum alloy compositions include the 3xx alloy compositions and the 4xx alloy compositions of the Pink Sheets.

A 5xxx aluminum alloy is an aluminum alloy comprising magnesium (Mg) as the predominate alloying ingredient, except for aluminum. The 5xxx aluminum alloy compositions include the 5xx alloy compositions of the Pink Sheets.

A 6xxx aluminum alloy is an aluminum alloy comprising both silicon and magnesium, and in amounts sufficient to form the precipitate Mg₂Si.

A 7xxx aluminum alloy is an aluminum alloy comprising zinc (Zn) as the predominate alloying ingredient, except for aluminum. The 7xxx aluminum alloy compositions include the 7xx alloy compositions of the Pink Sheets.

The 8xxx aluminum alloy compositions include the 8xx alloy compositions and the 9xx alloy compositions of the Pink Sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system for continuously casting heat-treatable aluminum alloy plate via a horizontal belt caster (1) and a quenching apparatus (3) located proximal the exit of the horizontal belt caster (1).

FIG. 2 is a graph showing testing results of Example 1.

FIG. 3 is a graph showing testing results of Example 2.

DETAILED DESCRIPTION Example 1—Lab Scale Trials

A horizontal belt caster was used to produce a 4.4 inch (11.18 cm) 6xxx aluminum alloy as-cast plate from a mixture of scrap. After casting, lab-scale sections of as-cast plate were solutionized at 980° F. for 5 minutes in a lab-scale furnace, and then quenched using three different methods: (a) still air, (b) forced air jets and (c) cold water quenching. The materials were then artificially aged at 365° F. for 18 hours. Material properties of the as-cast and artificially aged plate were then determined in accordance with ASTM B557, the results of which are shown in Table 1, below. As shown, heat-treatable alloys were produced from the mixture of scrap, the artificially aged products being substantially stronger than the naturally aged products. The full artificial aging curves (shown in FIG. 2) show that the scrap-based alloy, when properly solutionized and quenched, exhibits the potential for age hardening.

TABLE 1 Example 1 Results (ksi and MPa) Elonga- Speci- Yield Tensile Yield Tensile tion 4D men Quench Aging Strength Strength Strength Strength or 4W Number Method Method (ksi) (ksi) (MPa) (MPa) (%) 1 Still Natural 11.9 20.7 82 143 6.5 Air Age 2 Forced- Natural 13.0 22.3 90 154 5.3 Air Age 3 CWQ Natural 19.5 30.2 134 208 6.2 Age 4 Forced- Artif. 15.3 24.4 106 169 5.8 Air Age 5 CWQ Artif. 39.7 40.7 274 281 1.6 Age

Example 2—Industrial-Scale Quenching and Aging

A horizontal belt caster was used to produce a 2.225 inch (5.65 cm) as-cast plate from a mixture of 3xxx, 4xxx, 5xxx and 6xxx aluminum alloys. Upon exiting the horizontal belt caster, the as-cast plate was quenched using air knives, supplied by a high volume blower, which directed a continuous blast of ambient air onto the upper and lower surfaces of the as-cast plate. As the plate moved continuously from the caster to the flying saw (FIG. 1), the surface temperature was measured at fixed positions from the caster exit. Using these temperature readings and the casting speed, the plate surface temperature was plotted against time, the results of which are given in Table 2, below, and shown in FIG. 3. Samples from each condition were subsequently artificially aged at 365° F. for 8 hours. Material properties were then measured, the results of which are given in Table 3, below. As shown, increased yield strength is realized using forced air cooling (imposed immediately upon exiting the continuous caster) and the surface temperature of the plate is reduced.

TABLE 2 Example 2 Cooling Rate Results Blower Time Time Time Time Specimen Rate (1) (1) (2) (2) Time (3) Temp. (3) Number (RPM) (min) (° F.) (min) (° F.) (min) (° F.) 1 0 1.2 900 6.5 865 8.8 832 2 1125 1.1 818 5.8 613 7.9 613 3 1125 1.2 802 6.7 620 9.1 580 4 1125 1.3 751 7.1 575 9.7 525 5 1700 1.3 762 7.1 510 9.7 446 6 2250 1.3 724 6.9 482 9.4 440

TABLE 3 Example 2 Results (ksi and MPa) Blower Yield Tensile Yield Tensile Specimen Rate Strength Strength Strength Strength Elongation Number (RPM) (ksi) (ksi) (MPa) (MPa) (%) 1 0 18.1 25.1 125 173 2.6 3 1125 25.5 30.5 176 210 2.0 4 1125 25.8 28.5 178 196 1.3 5 1700 35.3 36.0 243 248 1.0 6 2250 33.1 35.5 228 245 1.5

While various embodiments of the new technology described herein have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the presently disclosed technology. 

What is claimed is:
 1. A method comprising: (a) continuously delivering a molten aluminum alloy to a horizontal belt caster; (i) wherein the molten aluminum alloy comprises a sufficient amount of at least one of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu) to promote formation of strengthening precipitates; (b) continuously solidifying the molten aluminum alloy into an aluminum alloy plate via the horizontal belt caster; (c) continuously discharging the aluminum alloy plate from an exit of the horizontal belt caster at a rate of from 1 inch to 20 inches per minute; (i) wherein the discharged aluminum alloy plate has a gauge of from 0.25 inch to 5.0 inches; (d) quenching the discharged aluminum alloy plate via a quenching apparatus located proximal the exit of the horizontal belt caster, thereby producing an as-cast heat-treatable aluminum alloy plate; (i) wherein the quenching comprises contacting outer surfaces of the discharged aluminum alloy plate with a quenching media.
 2. The method of claim 1, further comprising: artificially aging the as-cast heat-treatable aluminum alloy plate, thereby developing strengthening precipitates within the as-cast heat-treatable aluminum alloy plate.
 3. The method of claim 2, wherein the strengthening precipitates are coherent phases comprising silicon, copper, magnesium and/or zinc.
 4. The method of claim 3, wherein the as-cast heat-treatable aluminum alloy plate comprises a sufficient amount of the strengthening precipitates to realize a peak strength (T6) that is at least 5 ksi higher than the naturally aged strength (T3).
 5. The method of claim 2, wherein the as-cast heat-treatable aluminum alloy plate comprises an as-cast grain structure, the method comprising maintaining the as-cast grain structure of the heat-treatable aluminum alloy plate; wherein, after the artificially aging step, the heat-treatable aluminum alloy plate comprises the as-cast grain structure with the strengthening precipitates.
 6. The method of claim 5, comprising: providing the as-cast heat-treatable aluminum alloy plate to a customer, wherein the as-cast heat-treatable aluminum alloy plate comprises the as-cast grain structure and the strengthening precipitates.
 7. The method of claim 5, wherein the maintaining step comprises forgoing hot or cold working of the as-cast heat-treatable aluminum alloy plate after the continuously casting step.
 8. The method of claim 1, comprising: melting an aluminum alloy scrap feedstock, thereby producing the molten aluminum alloy; wherein the aluminum alloy scrap feedstock comprises a combination of scrap of at least two different aluminum alloys.
 9. The method of claim 8, wherein the at least two different aluminum alloys are at least two different classes of aluminum alloys.
 10. The method of claim 9, wherein the at least two different classes of aluminum alloys are selected from the following aluminum alloy series: 1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, and 8xxx aluminum alloys.
 11. The method of claim 9, wherein the at least two different classes of aluminum alloys are selected from the following aluminum alloy series: 3xxx, 4xxx, 5xxx, 6xxx, and 7xxx aluminum alloys.
 12. The method of claim 9, wherein the at least two different aluminum alloys are selected from the group consisting of 3xxx, 4xxx, 5xxx, and 6xxx aluminum alloy scrap.
 13. The method of claim 8, wherein the at least two different aluminum alloys are from the same class of aluminum alloys.
 14. The method of claim 13, wherein at least two different aluminum alloys are both 6xxx aluminum alloys.
 15. The method of claim 13, wherein the two different aluminum alloys are both 7xxx aluminum alloys.
 16. The method of claim 13, wherein the at least two different aluminum alloys are both 2xxx aluminum alloys.
 17. The method of claim 1, wherein the discharged aluminum alloy plate is one of a 2xxx, 6xxx, 7xxx, and 8xxx(HT) aluminum alloy plate.
 18. An as-cast aluminum alloy plate having a thickness of from 0.25 inch to 5.0 inches; wherein the as-cast aluminum alloy plate comprises at least 0.5 wt. % of at least one at least one of zinc (Zn), magnesium (Mg), silicon (Si), and copper (Cu); wherein the as-cast aluminum alloy plate has a dendritic microstructure; wherein the as-cast aluminum alloy plate has a secondary dendritic arm spacing of from 30 to 150 microns in all of the longitudinal (L), the long-transverse (LT) and the short-transverse (ST) directions of the as-cast aluminum alloy plate; wherein the as-cast aluminum alloy plate has equiaxed grains and is free of elongated grains. 